Eriocaulon compressum is polymorphic in habit. Male flowers vary considerably in length and degree of connation, and female flowers are often sterile. Of the southeastern coastal plain species this and the similar, but proportionately smaller, E. lineare, are the most aquatic, the former most common around clay-based ponds, the latter around karst ponds. Unlike the more northern E. aquaticum, these two species seldom frequent the shallows of flowing streams.